Generally, two different duplex modes are employed for separating the transmission directions from the user to the base station and back: Frequency Division Duplex (FDD) and Time Division Duplex (TDD). In the TDD mode, a single bandwidth is shared between uplink (UL) and downlink (DL), with the sharing being performed by allotting different periods of time to uplink and downlink.
Taking a Long Term Evolution (LTE) or LTE-Advanced (LTE-A) TDD system for example, there are seven different patterns of uplink/downlink switching, termed uplink-downlink configurations 0 through 6, each of them having a different DL and UL allocation between each other. The LTE TDD system allows for asymmetric UL-DL allocations by the seven different uplink-downlink configurations. Generally, the LTE TDD system statically or semi-statically allocates the UL-DL configuration among cells. Conventionally, all neighboring cells have the same uplink-downlink configuration, e.g., configuration 0, after configurations of the cells are deployed by the LTE TDD system. The configuration allocation is not changed during operation (static allocation) or is changed after years of operation (semi-static allocation).
In some scenarios, the static or semi-static allocation may not match the burst traffic conditions, e.g., the FTP traffic. Accordingly, dynamic configuration allocation is proposed for matching the traffic conditions better. As such, the neighboring cells may have different uplink-downlink configurations from each other. By dynamically allocating UL-DL configurations to different cells, asymmetric DL and UL traffic demands may be well handled.
However, freely adjusting each cell's UL-DL configuration may result in significant cross-subframe interference, e.g., Cross-subframe Co-channel Interference (CCI), including both BS-BS CCI and UE-UE CCI, which would significantly degrade the system performance. This CCI is brought by the opposite-direction transmissions in neighboring cells when dynamic UL-DL configuration/reconfiguration is enabled.
Since the BSs usually have higher transmission power and more transmit antennas than the UEs, the BS-BS interference is more severe than the UE-UE interference. Therefore, there is a need to find interference avoidance/mitigation schemes for eliminating the negative impact on the system performance arising from the BS-BS CCI.